Hello Silvija, welcome! What a brilliant vision.
I agree with Maggi - buy lots of the commercially available varieties to see what works for you. This will give you instant impact, and meanwhile you can grow more from seed. Commercial growers can supply bulbs in the quantities you will need - I have had good results in the past from Eurobulb (
www.eurobulb.nl). I don't know what would work best in your area but here in the UK the best crocus for naturalising are C. tommasinianus and C. chrysanthus.
If you are creating a bulb lawn you might want to think about other flowers to extend the interest - Scilla, Ornithogalum, Chionodoxa, tulips, narcissi and fritillaries can all extend the season when the crocuses have finished flowering. Lots of options!
Best wishes, Tristan